This invention relates to an improvement in an exhaust system for a multi-cylinder internal combustion engine, and more particularly to an improvement in an exhaust manifold to which a catalytic converter is directly connected.
It has been proposed to directly connect a catalytic converter for purification of engine exhaust gas to a branch runner gathering section of an exhaust manifold in view of relatively narrow engine compartment space and from the standpoint of engine compartment layout. Although such a proposition gives an advantage that the temperature of exhaust gas to be supplied to the catalytic converter is maintained higher to improve the purification by the catalyst, it is difficult to so supply the exhaust gas so as to be uniformly dispersed over the entire catalyst. Particularly in a case where a honeycomb type monolithic catalyst is used in the catalytic converter connected to the exhaust manifold branch runner gathering section, unless the exhaust gas is uniformly dispersed over the entire upstream or inlet end surface of the catalyst, the catalyst is excessively locally heated, which results in deteriorated catalytic performance and thermal damage of the catalyst, thereby losing the desired functions of the catalyst. As discussed above, good dispersion of the exhaust gas over the entire end inlet surface of the catalyst has been earnestly required.